Device for attenuating noise emitted by the jet of a jet engine

ABSTRACT

The noise emitted by the jet of a jet engine is suppressed or in any event attenuated by a blading fitted in the exit section of the jet engine nozzle and designed with a lift-producing profile adapted, by virtue of said lift, to create a series of tip vortices level with and at the periphery of the blading.

United States Patent Inventor Andre Labussiere Fontenay-le-Fleury, France Appl. No. 53,224 Filed July 8, 1970 Patented Oct. 19, 1971 Assignee Avions Marcel Dassault Vaucressou, France Priority July 16, 1969 France 69 24196 DEVICE FOR ATTENUATING NOISE EMITTED BY THE JET OF A JET ENGINE 7 Claims, 4 Drawing Figs.

U.S. Cl 181/33 HC, 181/33 HD, 239/265.13,239/265.19,181/58 Int. Cl F0ln 1/08,

[50] Field of Search 181/33, 33.22, 33.221, 33.222, 43, 51, 58; 239/l27.3, 265.11, 265.13, 265.17, 265.19, 265.23

[56] References Cited UNITED STATES PATENTS 2,934,889 5/1960 Poulos 181/33 HD 2,944,623 7/1960 Bodine 181/33 HC 3,153,319 10/1964 Youngetal. 181/33 HC FOREIGN PATENTS 885,093 12/1961 Great Britain 181/33 HC Primary ExaminerRobert S. Ward, J r.

-Attorney-William J. Daniel ABSTRACT: The noise emitted by the jet of a jet engine is suppressed or in any event attenuated by a blading fitted in the exit section of the jet engine nozzle and designed with a liftproducing profile adapted, by virtue of said lift, to create a series of tip vortices level with and at the periphery of the bladmg.

DEVICE FOR A'ITENUA'IING NOISE EMIT'IED BY THE JET OF A JET ENGINE Those skilled in the art will be aware that the noise produced by aircraft jet engines is due in major part to pressure and velocity fluctuations crated by the shear effect between the jet or internal high-velocity flow and the surrounding atmosphere or external flow which has a relatively low velocity.

In the case of a supersonic jet, interactions between the turbulence thus generated and the shock waves, complicate this phenomenon.

It has already been proposed that this noise be attenuated by various arrangements which enable the mixing between the internal and external flows to be improved, for example by a venturi effect, by subdivision and interleaving of the flows.

The object of the invention is an improved silencer device which promotes mixing between the internal and external flows and introduces substantial improvements compared with the known devices both as far as the attenuation of the noise level is concerned and as far as concerns the jet engine performance.

In accordance with the invention, there is arranged, in the exit section of the jet engine nozzle, a blading system with a lift profile designed by virtue of the lift effect to produce a series of marginal vortices at the level of and at the periphery of the blading.

The axes of these vortices being substantially parallel to the nozzle axis, they induce substantial radial velocity components which facilitate exchanges between the potential cone of the jet and the exterior, and this diminish the emitted noise level. This silencer in fact operates by a mechanism of induced dilution brought about by the blade lift. A favorable supplementary effect from the acoustic point of view can be attributed to the fact that, additionally, the jet is split up by the blading.

In accordance with a preferred embodiment of the invention, the blading in question is constituted by a series of radial blades distributed around a central body, although other arrangements can equally well be adopted, for example a louvre arrangement.

The ensuing description which relates to the accompanying drawing, given her by way of a nonlimitative example, will indicate how the invention may be carried into practice.

In the drawings:

FIG. I is a schematic perspective view of a jet engine nozzle equipped with the silencer in accordance with the invention.

FIGS. 2, 3, and 4 are diagrams illustrating a variant embodiment with a reverse thrust system, FIGS. 3 and 4 respectively providing views in axial section and elevation (in the latter case on tee rear of the nozzle).

In the embodiment of FIG. 1, the jet engine nozzle 1 contains a central body 2 from which extend radial blades 3 which advantageously project to the rear of the exit plane of the nozzle. These blades are not assembled on simple symmetrical profiled arms designed in order to reduce drag; in other words, they are true blades or aerofoils which have a top camber and bottom camber and give rise to an aerodynamic lift Rz due to the jet flow. It is this lift which in fact produces, as with an aerofoil, marginal or tip vortices illustrated schematically by the arrows 4 and extending through vortex zones 5.

These vortices promote the mixing and reciprocal penetration of the stream lines of the gas of the internal flow and those of the ambient air of the external flow.

This kind of silencer has an obvious advantage because of its simplicity and robustness. It can easily be designed to be wholly or partially retracted in cruising flight.

In the embodiment shown in FIG. 2, the blades have a variable camber. Each blade is made up on the one hand by a fixed front element 3a at the leading edge and situated in the body of the jet, the direction of which latter is indicated by the arrow F, and on the other hand by a movable trailing edge flap 3b articulated about a radial axis 6.

At A, dotted lines have been used to illustrate the cruising position in which the flap 312 forms a projection of the fixed part 30, in this position the blade lift being virtually zero, whilst the reference D indicates in chain-dot the silencing position in which the flap 3b is deployed to give sutficient chamber for lift.

In accordance with one feature of the invention, this variable camber bladingis integrated into a reverse thrust system for the jet. FIG. 3 illustrates a reverse thrust system of conventional kind in which a grid of deflector blades 7 is located in a lateral duct 8 which can be closed off during nonnal operation and uncovered on landing when it is desired to produce reverse thrust for braking, by forward deflection of the jet. At this moment, the trailing edge flaps 3b are deployed through about in relation to the fixed part 3a, into the position C shown in full line in FIG. 2, and virtually close off the exit section of the nozzle 1, as shown in FIG. 4. The hot gases are then forced to escape through the lateral duct 8 (FIG. 3) and are deflected forward by the blade grid 7.

It will be appreciated that the embodiments described are merely examples and are open to modification in various ways without in so doing departing from the scope of the invention, which is defined in the appended claims. In particular, instead of employing partially fixed and partially movable blades, as in the embodiment shown in FIGS. 2, 3 and 4, it would be possible to use unitary blades which are pivotable as a whole.

1 claim:

1. In the exit section of a jet propulsion nozzle, a device for attenuating the noise emitted by the jet issuing therefrom, comprising a blading fitted in said exit section and having blades shaped with a lift-producing profile and designed, by virtue of said lift, to create a series of tip vortices level with and at the periphery of the blading.

2. A device as claimed in claim-1, in which the blading is constituted by a series of radial blades distributed about a central body.

3. A device as claimed in claim I, in which the blading projects towards the rear of the exit plane of the nozzle.

4. A device as claimed in claim 1, in which the blading has a variable camber, each blade comprising on the one hand a fixed leading edge element and on the other hand a movable flap at the trailing edge.

5. A device as claimed in claim 4, in which the trailing edge flap can be disposed in projection of the fixed leading edge element, the assembly then being located in the body of the jet and the blade lift being virtually zero, the silencing effect being produced by deploying the trailing edge flap through a given angle in relation to the fixed part of the blade.

6. A device as claimed in claim 4, in which the trailing edge flaps can be deployed through approximately 90 in relation to the leading edge element in order to close off the exit section of the jet engine nozzle at least to a substantial extent.

7. A device as claimed in claim 6, in which auxiliary means are provided in order to enable the hot gases to escape laterally from the nozzle when its section is closed off and be deflected forward in order to create a reverse thrust. 

1. In the exit section of a jet propulsion nozzle, a device for attenuating the noise emitted by the jet issuing therefrom, comprising a blading fitted in said exit section and having blades shaped with a lift-producing profile and designed, by virtue of said lift, to create a series of tip vortices level with and at the periphery of the blading.
 2. A device as claimed in claim 1, in which the blading is constituted by a series of radial blades distributed about a central body.
 3. A device as claimed in claim 1, in which the blading projects towards the rear of the exit plane of the nozzle.
 4. A device as claimed in claim 1, in which the blading has a variable camber, each blade comprising on the one hand a fixed leading edge element and on the other hand a movable flap at the trailing edge.
 5. A device as claimed in claim 4, in which the trailing edge flap can be disposed in projection of the fixed leading edge element, the assembly then being located in the body of the jet and the blade lift being virtually zero, the silencing effect being produced by deploying the trailing edge flap through a given angle in relation to the fixed part of the blade.
 6. A device as claimed in claim 4, in which the trailing edge flaps can be deployed through approximately 90* in relation to the leading edge element in order to close off the exit section of the jet engine nozzle at least to a substantial extent.
 7. A device as claimed in claim 6, in which auxiliary means are provideD in order to enable the hot gases to escape laterally from the nozzle when its section is closed off and be deflected forward in order to create a reverse thrust. 